1. Field of the Invention
The present invention relates to an association complex comprising pullulan and polyethylene glycol, and preparation and uses of the same.
More particularly, the present invention relates to an association complex comprising pullulan and polyethylene glycol wherein the pullulan and polyethylene glycol exert a decreased solubility in water.
Polyethylene glycol will hereinafter be abbreviated as "PEG", and the association complex with pullulan will be designated as "association complex".
2. Description of the prior art
Pullulan is a viscous glucan produced by culturing a microorganism of the species Aureobasidium pullulans on a nutrient culture medium containing saccharide(s) such as monosaccharide and lower oligosaccharide under aerobic conditions. Hayashibara Co., Ltd., Okayama, Japan, is the sole company that commercializes pullulan on an industrial scale.
Since pullulan has characteristic properties such as water-solubility, edibility, transparency, oil-resistance, gas-barrier property, gloss and adhesion, it has been extensively used as a base material for foods, beverages, cosmetics and pharmaceuticals, as well as to prepare various shaped articles, for example, granule, tablet, rod, film and sheet.
Recently, as in the case of shaped articles for pharmaceutical uses, gradually disintegrable shaped articles that are imparted with controlled solubility and disintegration rate in a hydrous system in order to retain their efficacy over a prescribed period, and also sustained release shaped articles that gradually release the effective ingredient have been in great demand.
Although shaped articles containing intact pullulan are characterized in that they smoothly dissolve and disintegrate in water, these properties render the preparation of gradually disintegrable- and sustained release-shaped articles with pullulan very difficult.
To improve this, the present inventors propose in Japanese Patent Laid-Open No. 219,237/85 a shaped article wherein a heteromannan is incorporated together with pullulan.
Such shaped article has the demerits that its preparation is relatively complicated, as well as that the solubility may be still too high, dependent on the use.